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Cyclic microevolution with cyclic weather


Posted by DLH at , PBS Nova Discussion on Judgment Day,
The Design of Life, Nov. 13, 2007

It appears that the predictive essence of (micro) evolution is summarized in the principles we learned in kinder garden. Namely:

The Grand Old Duke of York
The grand old Duke of York,
He had ten thousand men.
He marched them up to the top of the hill
And he marched them down again.

And when they were up, they were up;
And when they were down, they were down.
But when they were only halfway up,
They were neither up nor down!

Now applying this to Darwin’s Finches:

The Grand Old El Nino
The grand old El Nino
He drove ten thousand birds
He drove them out into a drought
And he drove them back again.

When those beaks are dry they’re thick
And when they’re wet their thin
And when they’re only half way dry
They’re neither thick nor thin.

This distribution in beak size and consequent cyclic variation with El Ninos can be predicted by the following design principle:

Provide variety and robustness.

Form distributions of genes (alleles) that give variations in beak size.

"When those beaks are dry they’re thick And when they’re wet their thin" #2. Magic Beaks or robust natural selection? The Grant's 2006 Study makes no mention of magic beaks. figment
The unpredictable variability of microevolution and the strong impact of birdsong imprinting was observed by the Grants in 2002.
"From 1972 to 2001, Geospiza fortis (medium ground finch) and Geospiza scandens (cactus finch) changed several times in body size and two beak traits. Natural selection occurred frequently in both species and varied from unidirectional to oscillating, episodic to gradual. Hybridization occurred repeatedly though rarely, resulting in elevated phenotypic variances in G. scandens and a change in beak shape. The phenotypic states of both species at the end of the 30-year study could not have been predicted at the beginning."
"All 23 G. scandens females paired with G. scandens males, but two of 115 G. fortis females paired interspecifically. All their F1 offspring later bred with G. scandens (43) because choice of mates is largely determined by a sexual imprinting-like process on paternal song (42)."
Grant PR, Grant BR. 2002. Unpredictable evolution in a 30-year study of Darwin's finches. Science 296:707-711.(subscription) (quoted by: John Hawks Hybridization among Darwin's finches) DLH
PaV Insufficient time for speciation from cyclic variation from El Nino cycles is a very important observation. For further details on Haldane's Dilemma see: Haldane's dilemma at ResearchID.org Socio-religious Selection Hypothesis: Among humans, socio/religious selection appears to dominate natural selection. Religion: People prefer to marry others of the same religion. Priests show strong affinity for others in the priestly class. e.g. Cohen among Jews, Brahmans among Hindus. Language: People prefer to marry others of the same language. Social level: People prefer to marry within their own social level - or relatives provide pressure to encourage marriage among similar social level. See Uptown vs downtown vs across the tracks. e.g., the cultural observations of My Fair Lady. Nobility: Nobility marrying within the noble class, with the privileges of nobility defined by lineage exemplifies lineage class selection. Royalty epitomize this tendency. Ethnic group: People prefer/are pressured to marry within their ethnic group. e.g., by skin color, hair color, facial features etc. Readers are welcome to add formal references to studies of these socio-religious selection observations. Bird song social selection Hypothesis: Birds may socially select based on song. Some groupings of Darwin's Finches appear to be based on social criteria, not physical speciation. The orthodox explanation is that beak size causes physical changes in bird song related to selective advantage. Vocal mechanics in Darwin's finches: correlation of beak gape and song frequency Jeffrey Podos1,*, Joel A. Southall1 and Marcos R. Rossi-Santos, Journal of Experimental Biology 207, 607-619 (2004) However, consider the following evidence on hybrid mating and bird song selection:
Our long-term field studies of banded birds on Daphne Major (Grant 1999) and Genovesa (Grant and Grant 1989) reveal that sympatric species (those on the same island) belonging to the same genus do hybridize, albeit rarely.
Both male and female hybrids respond to the song type of their fathers when they choose a mate. Only males sing, and they sing only one type of advertising song throughout their lives. If pairs form between species, say between a female ground finch and a male cactus finch, the offspring eventually mate with members of their father's species—in this case, other cactus finches. The sons will sing cactus finch songs, and the daughters will mate with males singing cactus finch songs. Morphology also plays a role in mate choice. On Daphne Major, an exceptional hybrid male that sang a cactus finch song but whose beak was closer in shape to that of a medium ground finch first mated with a cactus finch female and later with a medium ground finch female. Thus, visual and auditory cues appear to act in association.
Adaptive Radiation of Darwin's Finches Peter R. Grant, B. Rosemary Grant, American Scientist Vol. 90; No. 2 p 130; DOI: 10.1511/2002.2.130 This where physical attributes may provide some short term cyclic selectivity under cyclic variations in environment, how much of a quantitative impact do they have compared to social bird song selection etc? DLH
We had a discussion here sometime back about Haldane's dilemna; that is, the number of offspring that must 'die' in order to have a new allele (variant of a gene) become fixed in the species. I noted then that the beak size---if considered an allele that becomes fixed in the population---was changing too fast for it to be explained via population genetics, since the mutation rate needed for the allele to change as quickly as it had would require enormous amounts of the finches to die each year (which, it is safe to assume, would have been duly noted by biologists [and probably attributed to global warming!]). I agree that this swaying back and forth, or marching up and down, is beak size bespeaks a design for needed variation in a particular population experiencing changing environmental conditions. PaV
O bacterial flagellum, There's much you have to tell'em, About Design and Intelligence, Not random, stupid chance. cdesignproponentsists

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